Marking instrument



FIG. 1 is a side elevational view of a marking instrument showing my new design in an exploded condition, all other sides being identical;

FIG. 2 is a top perspective view with the cap member in place;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a marking instrument, as shown and described. 